Please do not panic, it does not seems to be gangrene
. it is a kind of bunt injury.Yes, it is normal for bruising colour to spread it will first spread, then localized, then will move towards edge and finally will erupt out. The presentation seems to be muscular trauma and ligament injury
. It otherwise is always recommended to get the injured part examined by a specialist and then the relevant investigation is called for.
Following is my advise to you:
1. Arnica Montana 30C 5 drops thrice daily for 5 days(Homoeopathic Medicine)
2. Use hot water fomentation
3. You can apply Volini
Gel or some other ointment to relieve pain
4. Make less movement of the involved joint.
5.If you find things worsening then contact your orthopedician
Wish you a speedy recovery to health